(1) Technical Field of the Invention
The present invention relates to an engine brake system featuring the provision of an oil pump designed for absorbing power, either in the inside or the outside of the engine and separately from the engine lubricating oil pump, to enable direct control of the speed of the crank shaft of the engine.
(2) Prior Art
For braking an engine, there is generally used an exhaust brake system in which the sectional area of the exhaust port of the engine is controlled by opening or closing a butterfly valve--which is provided in the exhaust pipe of the engine to block the exhaust port--to elevate the exhaust pressure in the cylinder to thereby enhance the effect of engine brake.
Regarding the engine braking system using an oil pump provided specifically for engine brake separately from the engine lubricating oil pump, there are known no other techniques than those disclosed in Japanese Utility Model Unexamined Publication Nos. 60-26244 and 62-105862 both of which had been filed by the applicant of the present application.
A wheel brake which is low in radiating capacity in comprison with heat build-up by the brake when the vehicle is running on a way with a long negative gradient tends to suffer from overheat in long time use, so that in such a case engine brake needs to be used.
The exhaust brake system, however, has the problem that in use with a supercharged engine, it may fail to effec sufficient brake of the engine. As a means for increasing the engine output, a super charger with an intercooler is used to elevate the engine output while keeping the cylinder capacity of the engine as small as possible, and in this case, when using an exhaust brake system which controls the engine output by narrowing the exhaust port of the engine, the engine output may not be lowered as desired even if the exhaust port of the engine is narrowed down.
On the other hand, in the case of the engine brake system disclosed in Japanese Utility Model Unexamined Publication No. 60-26244 in which a cut off valve for opening and closing the oil supply pipe is provided at the discharge port of the oil pump, and this cut off valve is operated in concert with the exhaust pressure receiving means to control the engine output, there is the problem that the rate of change engine braking torque for the variation of engine speed is not constant since the cut off valve is incapable of adjusting the oil feed in the oil supply pipe, that is, the cut off valve has no oil feed adjusting function. There is also the problem that the mechanism for operatively linking the cut off valve with the exhaust pressure receiving means is complicated.
Further, in the case of the engine brake system disclosed in Japanese Utility Model Unexamined Publication No. 62-105862 in which a by-pass valve closed during the application of engine brake is provided in a pipe connecting the discharge port and the intake port of oil pump, and the discharge port of said oil pump is connected to the intake port of the engine lubricating oil pump through an oil supply pipe throttling mechanism, there is the problem that mechanism for adjusting pressure in the oil supply pipe of the oil pump is too large to fit in the inside of the engine unit.